1. Field of the Invention
The present invention relates to a method for producing an ethylene-vinyl alcohol copolymer (hereinafter abbreviated as xe2x80x9cEVOHxe2x80x9d) resin composition.
2. Description of the Related Art
EVOH has a high gas barrier property and excellent oil resistance, aroma retention property, transparency, and the like. Due to these properties, EVOH is formed into films, sheets, bottles etc. and widely used for food packaging and the like.
Conventionally, various properties of EVOH have been improved by blending it with various other components. It has also been proposed that the EVOH and various components be melt-kneaded in an extruder. Although typically EVOH in a dry state is introduced into an extruder, JP05 (1993)-9334A discloses a method of using water-containing EVOH. In JP05 (1993)-9334A, EVOH pellets having a water content ranging from 20 wt % to 60 wt % and raw starch (corn starch with a water content of 12 wt %) are introduced into a Henschel mixer and mixed. The mixture is fed to a twin-screw extruder with a vent-port to be kneaded at a temperature of 120xc2x0 C., and melt-extruded in a strand form. The strand-like coagulate is pelletized by means of a pelletizer. However, when such a mixture containing the above-mentioned amount of water is melt-kneaded using a twin-screw extruder having no dewatering portion, free water is readily generated and as a result, the strands break immediately after being discharged from the extruder. This breakage makes it difficult to provide pellets having a stable shape. When the pellet shape is unstable, several problems may occur, for example, powder may be generated during transportation of the pellets thus causing thermal deterioration, or the powder may block in a hopper when the pellets are fed into a molding machine, resulting in surging.
The method of producing an EVOH resin composition according to the present invention comprises: introducing an EVOH resin having a water content of at least 0.5 wt %, preferably 0.5 wt % to 70 wt % (componentA) and an additional component (component B) into an extruder; kneading the components A and B while adjusting the water content of the resin composition in the extruder by feeding water to and/or removing water from the extruder; and discharging the resulting EVOH resin composition. Here, water is fed and removed as a liquid. Unless otherwise stated, the term xe2x80x98waterxe2x80x99 is used here to indicate liquid water and not water in non-liquid state such as water vapor.
The present invention provides an EVOH resin composition having a stable shape since the water content is adjusted before the composition is discharged by feeding water to and/or removing water from the extruder so as to suppress strand-breakage or the like.